Which part of the eye is responsible for admitting light?

The cornea is primarily responsible for admitting light into the eye. As the outermost transparent layer of the eye, the cornea allows light rays to enter and begins the process of focusing the light onto the retina. It plays a crucial role in the eye's refractive power, working in conjunction with the lens to ensure that light is directed appropriately for optimal vision.

While the pupil also functions as an opening that regulates the amount of light entering the eye, it is the cornea that acts as the first point of contact for light. The lens, located behind the pupil, fine-tunes the focus of light after it has passed through the cornea. The iris controls the size of the pupil and thus regulates light by adjusting how wide the pupil opens or closes in response to varying light conditions, but it does not directly admit light into the eye.